1. Field of the Invention
The present invention relates to an acceleration sensor for determining vehicular acceleration, the sensor being used in electronically controlled braking systems of automobiles and other vehicles, for example.
2. Description of the Related Art
A conventional acceleration sensor includes a magnetic fluid sealed in a case and movable in the acceleration direction, a fixed permanent magnet magnetizing the magnetic fluid, and a coil for detecting deformation of the magnetic fluid. The displacement of the magnetic fluid determines the magnitude of electromotive force generated at the coil, which constitutes a differential transformer, and the magnitude of the electromotive force determines the displacement of the magnetic fluid and detects the acceleration. See, for example, Japanese Unexamined Patent Publication (Kokai) No. 60-133370.
In the above acceleration sensor of the prior art, however, the magnetic fluid vibrates in the air or other medium and thus air bubbles and liquid bubbles or the like are easily formed. Further, a complicated construction is required to facilitate the deformation of the magnetic fluid, and since the sensor operates on the principle of detecting changes in the shape of the magnetic fluid, a problem arises in that the sensor is very susceptible to the effects of changes in viscosity and an expansion of volume due to temperature changes.